// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CC_BASE_HISTOGRAMS_H_
#define CC_BASE_HISTOGRAMS_H_

#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/metrics/histogram_base.h"
#include "base/metrics/histogram_macros.h"
#include "base/numerics/safe_math.h"
#include "base/strings/stringprintf.h"
#include "base/time/time.h"
#include "base/timer/elapsed_timer.h"
#include "cc/base/cc_export.h"

namespace cc {

// Supplies a client name to be inserted into histogram names.
// These are known so far: Renderer, Browser
//
// We currently assume that there is only one distinct client per process.
// Not thread-safe. If called multiple times, warns and skips metrics.
CC_EXPORT void SetClientNameForMetrics(const char* client_name);

// Returns the client name, for use by applicable cc metrics code.
// May return null, in which case no clients, or at least two clients, set the
// client name, and these metrics should be omitted.
//
// This method guarantees that it will never return two distinct non-null
// values over the lifetime of the process.
const char* GetClientNameForMetrics();

// Emits UMA histogram trackers for time spent as well as area (in pixels)
// processed per unit time. Time is measured in microseconds, and work in
// pixels per millisecond. Histogram name should include a %s to grab the client
// name.
//
// Usage:
//   // Outside of a method, perhaps in a namespace.
//   DEFINE_SCOPED_UMA_HISTOGRAM_AREA_TIMER(
//       ScopedReticulateSplinesTimer,
//       "Compositing.%s.ReticulateSplinesUs",
//       "Compositing.%s.ReticulateSplinesPixelsPerMs");
//
//   // Inside a method.
//   ScopedReticulateSplinesTimer timer;
//   timer.AddArea(some_rect.size().GetArea());
//
#define DEFINE_SCOPED_UMA_HISTOGRAM_AREA_TIMER(class_name, time_histogram,        \
    area_histogram)                                                               \
    class class_name : public ScopedUMAHistogramAreaTimerBase {                   \
    public:                                                                       \
        ~class_name();                                                            \
    };                                                                            \
    class_name::~class_name()                                                     \
    {                                                                             \
        Sample time_sample;                                                       \
        Sample area_sample;                                                       \
        const char* client_name = GetClientNameForMetrics();                      \
        if (client_name && GetHistogramValues(&time_sample, &area_sample)) {      \
            /* GetClientNameForMetrics only returns one non-null value over */    \
            /* the lifetime of the process, so these histogram names are */       \
            /* runtime constant. */                                               \
            UMA_HISTOGRAM_COUNTS(base::StringPrintf(time_histogram, client_name), \
                time_sample);                                                     \
            UMA_HISTOGRAM_CUSTOM_COUNTS(                                          \
                base::StringPrintf(area_histogram, client_name), area_sample, 1,  \
                100000000, 50);                                                   \
        }                                                                         \
    }

// Version of the above macro for cases which only care about time, not area.
#define DEFINE_SCOPED_UMA_HISTOGRAM_TIMER(class_name, time_histogram)             \
    class class_name : public ScopedUMAHistogramAreaTimerBase {                   \
    public:                                                                       \
        ~class_name();                                                            \
    };                                                                            \
    class_name::~class_name()                                                     \
    {                                                                             \
        Sample time_sample;                                                       \
        Sample area_sample;                                                       \
        const char* client_name = GetClientNameForMetrics();                      \
        if (client_name && GetHistogramValues(&time_sample, &area_sample)) {      \
            DCHECK_EQ(0, area_sample);                                            \
            /* GetClientNameForMetrics only returns one non-null value over */    \
            /* the lifetime of the process, so these histogram names are */       \
            /* runtime constant. */                                               \
            UMA_HISTOGRAM_COUNTS(base::StringPrintf(time_histogram, client_name), \
                time_sample);                                                     \
        }                                                                         \
    }

class CC_EXPORT ScopedUMAHistogramAreaTimerBase {
public:
    void AddArea(const base::CheckedNumeric<int>& area) { area_ += area; }
    void SetArea(const base::CheckedNumeric<int>& area) { area_ = area; }

protected:
    using Sample = base::HistogramBase::Sample;

    ScopedUMAHistogramAreaTimerBase();
    ~ScopedUMAHistogramAreaTimerBase();

    // Returns true if histograms should be recorded (i.e. values are valid).
    bool GetHistogramValues(Sample* time_microseconds,
        Sample* pixels_per_ms) const;

private:
    static bool GetHistogramValues(base::TimeDelta elapsed,
        int area,
        Sample* time_microseconds,
        Sample* pixels_per_ms);

    base::ElapsedTimer timer_;
    base::CheckedNumeric<int> area_;

    friend class ScopedUMAHistogramAreaTimerBaseTest;
    DISALLOW_COPY_AND_ASSIGN(ScopedUMAHistogramAreaTimerBase);
};

} // namespace cc

#endif // CC_BASE_HISTOGRAMS_H_
